The clinical syndrome of Osteoarthritis, which is also known as degenerative arthritis or degenerative joint disease, is characterized by a loss of articular cartilage on adjacent bony surfaces resulting in discomfort, loss of motion, and functional impairment. In a similar fashion, inflammatory arthritis, for example, rheumatoid arthritis, may result in a loss of cartilage surfaces from both biochemical and mechanical reasons. Furthermore, an accelerated loss of cartilage can result from traumatic injury to bones and joints and promote posttraumatic arthritis. As the bony surfaces become less protected by cartilage, the patient experiences pain, motion limitation, potential joint instability, and eventual functional impairment. Due to a decreased movement resulting from the pain or joint changes, regional muscles may atrophy, and ligaments may become more lax. Osteoarthritis is the most common form of arthritis, but inflammatory and post-traumatic arthritis also affect millions of patients.
Arthritis of the carpometacarpal (CMC) joint or “basilar” joint of the thumb is the development of pathologic changes of the articular cartilage and surrounding bone at a patient's joint involving, but not limited to, the relationship between the thumb metacarpal and the trapezium (one of the carpal or wrist bones). The effects of basilar joint arthritis may include, for example, debilitating hand pain, swelling, and decreased strength and range of motion, making it difficult to do simple tasks. Further pathologic involvement of bones local to the trapezium bone is often seen in this syndrome. As with the other articular relationships of the trapezium bone, those with the scaphoid and trapezoid bones (other carpal or wrist bones) may also manifest similar pathologic changes of the articular cartilage and surrounding bone due to basilar thumb arthritis.
In a healthy carpometacarpal (CMC) or basilar joint of the thumb, the ends of the bones are covered by articular cartilage, thereby providing a natural cushion from compressive forces and are lubricated and nourished by joint (synovial) fluid secreted by specialized cells lining the joint capsule. When a patient suffers from arthritis of the thumb CMC or basilar joint, the cartilage degrades and the relationship between adjacent or opposing bones is no longer protected from compressive and shear forces by the healthy cartilage cover. This results in a series of mechanical and biochemical alterations that result in pain, limited motion, instability, and deformity.
Treatment options for CMC or basilar thumb arthritis include, for example, splints (temporary immobilization of the patient's basilar joint), medication, corticosteroid injections, and surgery. Surgical treatments are typically of two general forms: motion-eliminating and motion-sparing options. The motion-eliminating alternative includes an arthrodesis or a fusion of the bones, thus completely sacrificing all motion between two bones through their respective joint surfaces by promoting bone growth across the former articulation.
Motion-sparing treatments may include, for example, simple removal of diseased bones (with or without accompanying soft tissue stabilization procedures) or removal of diseased bones and subsequent replacement (arthroplasty) of certain bones in the affected joint with biologic and non-biologic implants. More particularly, for CMC or basilar joint arthritis of the thumb, the trapezium bone of the patient's basilar joint may be partially removed (subtotal excision) or totally removed (total excision) to relieve the discomfort and mechanical problems associated with arthritis. The void created by either partial or complete excision of the joint shared by the trapezium and metacarpal bones (or other local carpal bones, as described) can then be left in that state or the resulting void can be filled by biologic or non-biologic material, i.e. an arthroplastic implant.
An approach to bone and joint implants is disclosed in U.S. Pat. No. 4,164,793 to Swanson, which discloses a lunate bone implant. The implant includes a body and a stabilizing stem extending therefrom. Another approach is disclosed in U.S. Pat. No. 4,198,712 to Swanson, which discloses a scaphoid bone implant. This implant also includes a body and a stabilizing stem extending therefrom.
An approach to a CMC or basilar joint implant is disclosed in U.S. Pat. No. 5,645,605 to Klawitter. The implant includes a threaded shaft portion for coupling to the first metacarpal bone of the patient's hand, and an articulating portion coupled thereto for replacing the articulating portion of the trapezium bone.
Potential drawbacks to the disclosed basilar joint implants may include, for example, instability of the implant, i.e. the implant may become dislodged. Moreover, the implants may not be mechanically robust and may break down under constant wear and tear within the basilar joint. Moreover, after implantation, the patient may not be provided with the sufficient thumb motion.
More particularly, in basilar joint implants that replace the trapezium bone, the bases of the first and second metacarpal bones may impinge upon one another and cause the patient discomfort. Moreover, the implantation of such an implant may inadvertently change the length of the patient's thumb, i.e. foreshortening and telescoping of the osteo-articular column.